LeetCode-208.Implement Trie(Prefix Tree)

Implement a trie with insert, search, and startsWith methods.

Example:

Trie trie = new Trie();

trie.insert("apple");
trie.search("apple");   // returns true
trie.search("app");     // returns false
trie.startsWith("app"); // returns true
trie.insert("app");   
trie.search("app");     // returns true

Note:

You may assume that all inputs are consist of lowercase letters a-z.
All inputs are guaranteed to be non-empty strings.

使用数组保存子节点，但是不可扩展，效率高

使用ArrayList保存子节点，可扩展，但查找效率差

使用Map保存子节点

 1 class Trie {// mytip
 2     TrieNode root ;
 3 
 4     /** Initialize your data structure here. */
 5     public Trie() {
 6         root= new TrieNode();
 7     }
 8     
 9     /** Inserts a word into the trie. */
10     public void insert(String word) {
11         TrieNode cur = root;
12         if(null==cur){
13             cur = new TrieNode();
14         }
15         for (int i = 0; i < word.length(); i++) {
16             char c = word.charAt(i);
17             List<TrieNode> list = cur.children;
18             boolean flag = false;
19             for (int j = 0; j < list.size() ; j++) {
20                 if(list.get(j).val==c){
21                     cur = list.get(j);
22                     flag = true;
23                     break;
24                 }
25             }
26             if(!flag){
27                 TrieNode t = new TrieNode(c);
28                 cur.children.add(t);
29                 cur = t;
30             }
31         }
32         cur.isWord = true;
33     }
34     
35     /** Returns if the word is in the trie. */
36     public boolean search(String word) {
37         TrieNode cur = root;
38         for (int i = 0; i < word.length(); i++) {
39             char c = word.charAt(i);
40             if(null==cur||null==cur.children||0==cur.children.size()){
41                 return false;
42             }
43             List<TrieNode> list = cur.children;
44             boolean flag = false;
45             for (int j = 0; j < list.size() ; j++) {
46                 if(list.get(j).val==c){
47                     cur = list.get(j);
48                     flag =true;
49                     break;
50                 }
51             }
52             if(!flag){
53                 return false;
54             }
55         }
56         return cur.isWord;
57     }
58     
59     /** Returns if there is any word in the trie that starts with the given prefix. */
60     public boolean startsWith(String prefix) {
61         TrieNode cur = root;
62         for (int i = 0; i < prefix.length(); i++) {
63             char c = prefix.charAt(i);
64             if(null==cur||null==cur.children||0==cur.children.size()){
65                 return false;
66             }
67             List<TrieNode> list = cur.children;
68             boolean flag = false;
69             for (int j = 0; j < list.size() ; j++) {
70                 if(list.get(j).val==c){
71                     cur = list.get(j);
72                     flag =true;
73                     break;
74                 }
75             }
76             if(!flag){
77                 return false;
78             }
79         }
80         return true;
81     }
82 }
83 
84 class TrieNode{
85     List<TrieNode> children;//孩子结点使用List存放 效率较低
86     char val;
87     boolean isWord;
88     TrieNode(){
89         children = new ArrayList<>();
90         isWord = false;
91     }
92     TrieNode(char c){
93         children = new ArrayList<>();
94         isWord = false;
95         val =c;
96     }
97 }

 1 class Trie {//my
 2     TrieNode root ;
 3 
 4     /** Initialize your data structure here. */
 5     public Trie() {
 6         root= new TrieNode();
 7     }
 8     
 9     /** Inserts a word into the trie. */
10     public void insert(String word) {
11         TrieNode cur = root;
12         if(null==cur){
13             cur = new TrieNode();
14         }
15         for (int i = 0; i < word.length(); i++) {
16             char c = word.charAt(i);
17             Map<Character,TrieNode> list = cur.children;
18             if(list.containsKey(c)){
19                 cur = list.get(c);
20             }
21             else{
22                 TrieNode t = new TrieNode(c);
23                 cur.children.put(c,t);
24                 cur = t;
25             }
26         }
27         cur.isWord = true;
28     }
29     
30     /** Returns if the word is in the trie. */
31     public boolean search(String word) {
32         TrieNode cur = root;
33         for (int i = 0; i < word.length(); i++) {
34             char c = word.charAt(i);
35             if(null==cur||null==cur.children||0==cur.children.size()){
36                 return false;
37             }
38             Map<Character,TrieNode> list = cur.children;
39             if(list.containsKey(c)){
40                 cur = list.get(c);
41             }
42             else{
43                 return false;
44             }
45         }
46         return cur.isWord;
47     }
48     
49     /** Returns if there is any word in the trie that starts with the given prefix. */
50     public boolean startsWith(String prefix) {
51         TrieNode cur = root;
52         for (int i = 0; i < prefix.length(); i++) {
53             char c = prefix.charAt(i);
54             if(null==cur||null==cur.children||0==cur.children.size()){
55                 return false;
56             }
57             Map<Character,TrieNode> list = cur.children;
58             if(list.containsKey(c)){
59                 cur = list.get(c);
60             }
61             else{
62                 return false;
63             }
64         }
65         return true;
66     }
67 }
68 
69 class TrieNode{
70     Map<Character,TrieNode> children;//使用map存放子节点
71     char val;
72     boolean isWord;
73     TrieNode(){
74         children = new HashMap<>();
75         isWord = false;
76     }
77     TrieNode(char c){
78         children = new HashMap<>();
79         isWord = false;
80         val =c;
81     }
82 }

进阶题

单词搜索 LeetCode212 https://www.cnblogs.com/zhacai/p/10641592.html